This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-382551, filed Dec. 15, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a suspension for disc drive incorporated in an information processing apparatus, such as a personal computer.
In a disc drive that is provided with a rotating magnetic disc or magneto-optical disc, a magnetic head is used to record on or read data from a recording surface of the disc. The magnetic head includes a slider opposed to the recording surface of the disc, a transducer stored in slider, etc. When the disc rotates at high speed, the slider slightly lifts off the disc, whereupon an air bearing is formed between the disc and the slider. A suspension for holding the magnetic head comprises a beam member called a load beam, a flexure formed of a very thin plate spring fixed to the load beam, a base plate provided on the proximal portion of the load beam, etc. The slider that constitutes the magnetic head is mounted on the distal end portion of the flexure.
In a hard disc drive (HDD), the track center of the disc must be subjected to following control within xc2x110% of the track width. With the recent development of higher-density discs, the track width has been being reduced to 1 xcexcm or less, and it is hard to keep the slider in the track center. It is necessary, therefore, to carry out accurate position control of the slider as well as to increase the stiffness of the disc, thereby reducing the oscillation of the disc.
In general, conventional disc drives are of a single-actuator type such that a suspension is moved by means of a voice coil motor only. The single-actuator suspension has many peaks of resonance in low-frequency bands. Thus, it is hard to control a slider (head portion) on the distal end of the suspension in high-frequency bands by means of the voice coil motor only, and the bandwidth of a servo cannot be enhanced.
Accordingly, a dual-actuator suspension has been developed including a micro-actuator portion as well as a voice coil motor. The micro-actuator portion causes a second actuator slightly to move the distal end portion of a load beam or a slider in the transverse direction of the suspension (so-called sway direction).
Since the movable portion that is driven by means of the second actuator is considerably lighter in weight than a movable portion of the single-actuator suspension, the slider can be controlled in high-frequency bands. Thus, the dual-actuator suspension, compared with the single-actuator suspension, can make the bandwidth of a servo for the position control of the slider several times higher, and track misses can be reduced correspondingly.
It is known that a piezoelectric ceramic element, such as lead zirconate-titanate (solid solution of PbZrO3and PbTiO3) called PZT, can be suitably used as the material of the second actuator. Since PZT has a considerably high resonance frequency, it is suited for the second actuator that is used in the dual-actuator suspension. This piezoelectric ceramic element is fixed to an actuator base with an adhesive agent.
The piezoelectric ceramic element, e.g., PZT, used in the micro-actuator portion is as thin as tens to hundreds of micrometers and fragile. Electrodes for current supply to the piezoelectric ceramic element are formed on the obverse or reverse side of the element. On the other hand, the metal base plate and the like that constitute the actuator base are used as electrical grounds. In order to prevent a short circuit between the electrodes of the piezoelectric ceramic element and the actuator base, therefore, a clearance for electrical insulation must be secured between the electrodes and the actuator base. In general, this clearance is believed to be able to be secured by curing the adhesive agent in a manner such that the piezoelectric ceramic element and the actuator base are clamped in position by means of a jig.
If the piezoelectric ceramic element is clamped by means of the jig, however, it may be broken by stress, in some cases, since the adhesive agent slightly contracts as it cures. If the piezoelectric ceramic element is not broken in an adhesive bonding process, it may possibly be broken by the residual stress when it is subjected to external force in a bonding process or the like afterward.
Accordingly, the object of the present invention is to provide a suspension for disc drive designed so that piezoelectric ceramic elements can be securely insulated from an actuator base without being broken.
In order to achieve the above object, a suspension of the present invention comprises a load beam provided with a flexure, an actuator base provided on the proximal portion of the load beam, a piezoelectric ceramic element mounted on the actuator base and adapted to be distorted to displace the load beam in a sway direction when voltage is applied thereto, and an adhesive layer for fixing the piezoelectric ceramic element to the actuator base, the adhesive layer including an electrical insulating adhesive agent and a plurality of fillers of an electrical insulating material mixed in the adhesive agent and having a size such that a clearance for electrical insulation can be secured between the piezoelectric ceramic element and the actuator base. The fillers may suitably be formed of a material that has electrical insulating properties and cannot be easily deformed by compressive load, e.g., particles of silicon dioxide.
According to this invention, an appropriate clearance for electrical insulation can be easily secured between a conductive portion, such as an electrode, of the piezoelectric ceramic element and the actuator base. In this case, the adhesive agent can be cured by means of a jig without clamping the piezoelectric ceramic element, so that generation of stress can be avoided, and the piezoelectric ceramic element can be prevented from being broken.
In the suspension of the present invention, the actuator base may be formed having an opening portion capable of holding the piezoelectric ceramic element, the opening portion holding the piezoelectric ceramic element. Since the piezoelectric ceramic element is held in the opening portion of the actuator base, according to this invention, it can be protected, and a micro-actuator portion can be thinned. Since the deviation of the thickness-direction center of the piezoelectric ceramic element from that of a base plate is small, moreover, the displacement of the piezoelectric ceramic element can be transmitted effectively in the sway direction.
In the suspension of the invention, moreover, the piezoelectric ceramic element may be formed having different-polarity electrodes (first and second electrodes) individually on the obverse and reverse sides thereof. In the micro-actuator portion designed so that the first electrode of the piezoelectric ceramic element is grounded on the actuator base and a wire is bonded to the second electrode, according to this invention, an appropriate clearance for electrical insulation can be secured between the second electrode and the actuator base.
In the suspension of the invention, the recommended particle size of the fillers is 10 xcexcm or more, and preferably 30 xcexcm or more. According to this invention, good electrical insulating properties can be secured at high voltage, not to mention voltage that is applied to conventional piezoelectric ceramic elements.
Preferably, the Young""s modulus of the adhesive agent in a cured state is 60 MPa or more. Since the Young""s modulus of the adhesive agent is 60 MPa or more, according to this invention, the stroke of the piezoelectric ceramic element can be kept at a practically reasonable level. In this case, the Young""s modulus of the adhesive layer can be further improved if fillers with a Young""s modulus higher than that of the adhesive agent are mixed into the adhesive agent.
In the suspension of the invention, the load beam and the actuator base may be connected to each other by means of an independent flexible hinge member. According to this invention, materials that meet required properties of the load beam, actuator base, and hinge member can be used, so that the properties of the suspension can be improved.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.